96 CONTROLLED NATURAL SELECTION 
it is now only being introduced as a working 
hypothesis. It will probably not explain all 
cases of conspicuous colouring among parents, 
for it has been shown that conspicuous colour- 
ing may be used for other purposes. 
Attraction marks (see page 40, Chapter ITT) 
may be especially mentioned, for although 
they are conspicuous they are found in both 
parents and young. The rule appears to be: 
(1) vital parts that are conspicuously coloured 
in parents are protectively coloured in young, 
and (2) non-vital parts conspicuously coloured 
in parents are similarly coloured in young. 
A few examples are necessary: (1) The 
Goldfinch (Carduelis elegans): yellow bar 
across the wing, found in both parents and 
young; other conspicuous colours on vital 
parts of parents are not found in young, 
which are protectively coloured ; (2) Wheat- 
ear (Sazicola wnanthe): white rump present 
in both parents and young ; (3) Wood-pigeon 
(Columba palumbus): white patch on side of 
neck in parent, and because on a vital part, 
not present in young; (4) Mallard (Anasbascus): 
speculum on wing found in young and old, in 
all plumages. 
It appears, therefore, that some of the differ- 
ences in colour between parents and young, 
